1. Field of the Invention
This invention relates to a hydrotreating catalyst for a hydrocarbon oil and also to a process for hydrotreating the hydrocarbon oil by using the catalyst. More specifically, the present invention is concerned with a hydrotreating catalyst formed by having a hydrogenation-active component supported on a silica-alumina carrier and having a specific pore distribution and also with a hydrotreating process making use of the catalyst for the removal of sulfur compounds and nitrogen compounds from a hydrocarbon oil.
2. Background of the Invention
A variety of hydrotreating catalysts with oxides or sulfides of Group VI metals, Group VIII metals and the like of the Periodic Table supported on refractory inorganic oxides, such as alumina, silica-alumina, magnesia and zirconia, as carriers have been developed and widely used to date for the hydrotreatment of petroleum hydrocarbon oils. Such hydrotreating catalysts are used, for example, for the hydrodesulfurization, hydrodenitrogenation and hydrocracking of distillates and residual oils from atmospheric distillation or vacuum distillation processes, the hydrorefining of lubricant oil fractions, the hydrogenating isomerization of wax fractions, and the like. It has been increasingly recognized that the pores and pore distribution of a hydrotreating catalyst are important key factors for its activity and activity-maintenance ability in the hydrotreatment of various hydrocarbon oils. This recognition has therefore led to proposals such as a hydrotreating process making use of a catalyst, which has a pore distribution that the volume of pores having radii of 80 .ANG. and greater is limited to 10% or less of its overall pore volume, in order to prevent asphalt and metal-containing compounds from penetrating from a feed oil into its pores (see JP Kokoku 45-38142) and a hydrotreating process making use of a catalyst, in which pores having radii of 120 .ANG. and smaller are rather evenly distributed at intervals of 10 .ANG., in hydrodesulfurization of a residual oil (see JP Kokoku 4538143). In addition, a hydrodesulfurization catalyst for crude oil or topped crude is also disclosed, in which the volume of pores having diameters in a range of from 50 to 100 .ANG. is controlled at least 50% of the overall pore volume of the catalyst and the volume of pores having diameter in a range of from 0 to 50 .ANG. is controlled at most 25% of the overall pore volume of the catalyst (see JP Kokai 47-10356).
Further, the present applicant has also proposed a hydrotreating catalyst with a hydrogenation-active component such as molybdenum, cobalt or nickel supported on a silica-alumina carrier containing 2 to 40 wt. % of silica, in which the volume of pores having diameters of 300 .ANG. and smaller is controlled to account for 80% or more of the overall pore volume of the catalyst and the pores are controlled to distribute over both categories of micropores and macropores (see JP Kokoku 5-39662).
However, with a view to meeting the demand for more stringent hydrodesulfurization from the viewpoint of environmental conservation, the development of hydrodesulfurization catalysts, each of which contains pores of relatively small diameters in an increased volume and thus has a high specific surface area, has been the subject of a great deal of conventional work with a primary objective focused on improvements in desulfurization activity. As a corollary to this, there is an outstanding need for further improvements in denitrogenation activity.
Hydrocarbon oils include those containing nitrogen compounds, for example, basic nitrogen compounds such as pyridines, amines and amides and weakly acidic nitrogen compounds such as pyrroles at high levels. If these hydrocarbon oils are used as fuel oils as are, they become a cause of air pollution. This is certainly not preferred from the standpoint of environmental conservation. Further, catalytic cracking or catalytic reforming of a hydrocarbon oil with nitrogen compounds contained therein involves a problem that the nitrogen compounds cause a significant reduction in the activity of a cracking catalyst or reforming catalyst and hence induce a reduction in the yield of a product. It has therefore been an important theme to achieve high-efficiency denitrogenation of a hydrocarbon oil.
Incidentally, the attainment of highly distributed support of an active metal component on a carrier requires an increase in the specific surface area of the carrier. An increase in the volume of pores of relatively large pores effective for an improvement in denitrogenation activity, however, results in a problem that the specific surface area is decreased. Under such development situations, the development of a hydrotreating catalyst of a high surface area, which is excellent in both desulfurization activity and denitrogenation activity, has been strongly desired.
With the foregoing development situations, the present invention has as primary objects thereof the novel developments of a hydrotreating catalyst having both high desulfurization activity and high denitrogenation activity and a hydrotreating process of a hydrocarbon oil by using the hydrotreating catalyst.
With a view to attaining the above-described objects of this invention, the present inventors have proceeded with extensive research. As a result, it has been found that a hydrotreating catalyst with the volume of pores of relatively small diameters retained at a certain level and also with pores of relatively large, specific diameters increased in volume can promote a hydrodenitrogenation reaction and such a hydrotreating catalyst can be produced by controlling conditions for the preparation of an aluminum hydrate as a raw material component. The present inventors have also been interested in a finding that use of the hydrotreating catalyst makes it possible to effectively eliminate both sulfur compounds and nitrogen compounds from a hydrocarbon oil. Based on these findings, the present invention has come to completion.
The present invention relates in a first aspect thereof to a hydrotreating catalyst composed of a carrier, which is formed of silica-alumina containing silica in a proportion of from 2 to 40 wt. % based on the whole weight of the carrier, and at least one hydrogenation-active metal component supported on the carrier, characterized in that:
(1) the volume of pores having diameters in a range of from 30 to 100 .ANG. as measured by the nitrogen adsorption method accounts for 50 to 70% of the volume of pores having diameters in a range of from 0 to 150 .ANG. as measured by the nitrogen adsorption method, and the volume of pores having diameters in a range of from 100 to 150 .ANG. as measured by the nitrogen adsorption method accounts for 15 to 40% of the volume of pores having diameters in a range of from 0 to 300 .ANG. as measured by the nitrogen adsorption method; PA1 (2) the volume of the pores having the diameters in the range of from 0 to 300 .ANG. as measured by the nitrogen adsorption method accounts for at least 70% of the volume of pores having diameters of 40 .ANG. and greater as measured by the mercury porosimetry; and PA1 (3) the catalyst has a specific surface area of at least 200 m2/g. PA1 (1) the volume of pores having diameters in a range of from 30 to 100 .ANG. as measured by the nitrogen adsorption method accounts for 50 to 70% of the volume of pores having diameters in a range of from 0 to 150 .ANG. as measured by the nitrogen adsorption method, and the volume of pores having diameters in a range of from 100 to 150 .ANG. as measured by the nitrogen adsorption method accounts for 15 to 40% of the volume of pores having diameters in a range of from 0 to 300 .ANG. as measured by the nitrogen adsorption method; PA1 (2) the volume of the pores having the diameters in the range of from 0 to 300 .ANG. as measured by the nitrogen adsorption method accounts for at least 70% of the volume of pores having diameters of 40 .ANG. and greater as measured by the mercury porosimetry; and PA1 (3) the catalyst has a specific surface area of at least 200 m.sup.2 /g. As preferred embodiments, the present invention can provide: PA1 (III) a hydrotreating process of a hydrocarbon oil composed of a gas oil fraction as a principal component, characterized in that the hydrocarbon oil is brought into contact with hydrogen under hydrotreating conditions in the presence of the above-described hydrotreating catalyst.
The present invention also relates in a second aspect thereof to a process for the hydrotreatment of a hydrocarbon oil, characterized in that the hydrocarbon oil is brought into contact with hydrogen in the presence of the above-described hydrotreating catalyst.